Aim Given that urban landscapes often act as a point of entry for many non-native species and urban development continues to increase as the human population rapidly expands, an understanding of the interaction between urbanization and non-native plant species is important both in the control of potentially invasive species and in the conservation of native biodiversity. We investigated the spatial and temporal relationship between urban land cover and the distribution of non-native species in Britain using two floristic data sets collected at two different time periods: 1987–88 and 2003–04.

Location UK.

Methods Using floristic data collected by the Botanical Society of the British Isles in 1987–88 (Monitoring Scheme) and 2003–04 (Local Change) in conjunction with habitat data obtained from the Land Cover Map of the UK, we conducted multiple regression analyses both within and between years on both groups of species (natives, neophytes and archaeophytes) and individual species.

Results Neophytes (alien species introduced after 1500) were very strongly associated with urban land cover in both time periods and do not appear to be spreading out of urban habitats into the wider countryside. Archaeophytes (alien species introduced before 1500), however, showed a strong association with urban habitats in the earlier 1988 data set but no longer showed this association in the 2004 data set. Analysis at the individual species level showed that a large percentage of alien plant species, particularly archaeophytes, were not strongly associated with urban land cover or were negatively associated with such habitats.

Main conclusions Our results suggest that there has been a reduction in the urban association of archaeophytes that is likely to have resulted from the recovery of archaeophytes associated with non-urban (especially arable) habitats, following their decline in mid-20th century, rather than from the movement of aliens into the wider countryside from urban habitats.